1. Field of the Invention
The invention relates to the field of wireless communications, and specifically the invention relates to a method and system for dynamically allocating a set of broadcast TDMA channels to a network of transceiver nodes.
2. Description of the Prior Art
EPLRS (Enhanced Position Location Reporting System) is a legacy tactical communications radio system, and is currently used as the backbone of the lower Tactical Internet. EPLRS is a multi-channel TDMA radio system that provides different networking modes/services such as point-to-point circuit establishment and maintenance for unicast traffic, as well as multicasting/broadcasting for multicast/broadcast traffic. The networking mode of EPLRS that supports multicasting/broadcasting is called ‘EPLRS CSMA’. EPLRS CSMA can be described as a time slotted carrier sense multiple access (CSMA) system.
Referring to FIG. 1-A, the networks supported by EPLRS CSMA are dispersed over wide geographic areas resulting in a multi-hop network 10, since a given node can only reach other nodes located within its transmission range R 11. Therefore, in order to ensure reception of a transmission by all members of an EPLRS CSMA network, the transmission has to be relayed enough times so that even the radios furthest away from the source receive the transmission. With continued reference to FIG. 1-A, let NH 12 (Number_Hops) represent the worst case end-to-end hop distance between a source and a potential receiver.
Referring to FIG. 1-B, it then follows that every physical layer timeslot used to originate a transmission (referred to as a source timeslot 23) has to be followed by [NH−1] relay timeslots 24 that facilitate the end-to-end propagation of the transmission to the entire multi-hop network 10. The grouping of a source timeslot 23 and the [NH−1] relay timeslots 24 that follow the source timeslot is referred to as a physical layer TDMA frame 22. So, it can be seen that if all radios were within one hop of each other (i.e., fully-connected network) the physical layer TDMA frame length would be reduced to just one timeslot. With continued reference to FIG. 1-B, the 1st timeslot of a frame 23 is used by the winner(s) of the channel access contention to transmit a Transmission Unit (TU). Radios transmitting on the 1st timeslot 23 (i.e., the source timeslot) of a frame are referred to as source radios. The remaining [NH−1] relay timeslots 24 are used by the rest of the radios to flood-relay the received TU throughout the entire network. Flood-relaying works as follows: when a radio receives a particular TU for the first time, it will retransmit that TU in the following timeslot only. In other words, a given radio can relay a particular TU only once during a particular physical layer frame. When multiple radios are relaying simultaneously, potential receivers are able to capture one of the transmissions (usually the one closest to them), and treat the other transmissions as noise.
It is evident that the more geographically dispersed the network is, the larger the frame 22 length has to be in order to provide end-to-end (ETE) connectivity, resulting in a reduction of the effective TU throughput. For a frame length of NH timeslots, since only one TU is propagated throughout the network for every NH timeslots, the effective ETE TU Throughput (%) is equal to (1/NH)*100. For the rest of the invention presentation, we let NH be equal to 4. Then, it follows that the ETE TU throughput of an EPLRS CSMA 4-hop network is equal to 25%.